1. Field of the Invention
This invention relates to a method for reducing and possibly eliminating perfluorocarbon compounds (PFCs) gaseous emissions which produce global warming during fabrication of devices in the semiconductor and other industries.
2. Brief Description of the Prior Art
Due to the green house effect, there has been an industrywide commitment to reduce and possibly eliminate the causes of the green house effect. One such cause is emission into the atmosphere of perfluoro compounds also know as PFCs. The perfluorocarbons, such as but not limited to CF4, CHF3, C2F6, C3F8, SF6 and NF3, are known to have very high global warming potentials and governmental agencies have been and continue to seek ways to reduce the emissions of these compounds. Abatement techniques for perfluorocarbon emissions using heat or plasma are presently commercially available, however, most of the byproducts are still providing high global warming potentials as well as hazardous air pollutants and are relatively costly.
In the prior art, the gaseous effluent of procedures utilizing perfluoro compounds has generally been exhausted into the atmosphere, this being attributed as a cause of the green house effect or, alternatively, the use of fluorine-containing compounds has been restricted, either voluntarily or involuntarily, generally by substitution therefore of other materials. While this procedure is helpful, often the substituted materials provide inferior results as compared with the discarded fluorine-containing material which it replaced.
While thermal and plasma abatement units are presently available for use in the manufacture of semiconductors for removal of perfluorocarbon species, as stated above, the cost of such units and the unwanted byproducts developed by these units are still a material concern in the industry, especially by-products such as HF, which is a hazardous air pollutant, still regulated by the EPA. It is therefore apparent that improved procedures are required.
In accordance with the present invention, a method is provided for minimizing if not eliminating emissions of perfluorocompounds while retaining the use of such materials in a fabrication process by providing chemical trapping techniques to produce environmentally benign species, both by thermal and plasma source in a relatively inexpensive manner.
In the semiconductor industry, PFCs are used in the fabrication of semiconductor devices in both plasma etching and chamber cleaning sources after chemical vapor deposition (CVD) processes. No alternative fluorine sources have been found to replace the prior art PFC compounds with better or equivalent efficiency. The destruction efficiency for these compounds under a plasma reactor is low (from about 20 to about 30 percent) due to the recombination of the highly stable compounds, such as CF4.
Briefly, the above is accomplished by chemically trapping perfluorocarbon species by either plasma or thermal sources. A plasma or thermal source is provided at a downstream chamber in the fabrication process to break down the PFC emissions into highly reactive free radicals or ions along with trapping reagents, such as, but not limited to, iodine (I2), hydrogen iodide (HI), CH3I, C2H5I, CH3Br, bromine (Br2), C2H5Br, hydrogen bromide (HBr). The iodo and bromo carbon compounds are formed prior to the CF4 at a high energy stage, 800xc2x0 C. or higher, and before emission of the CF4 to the atmosphere. These high energy iodo and/or bromo compounds are reacted with the CF3 species prior to emitting to the atmosphere to produce by-products such as, but not limited to, and of the type CF3I, CF3Br. These iodo and bromo compounds have from about one tenth to about one one hundredth less global warming potential than do standard PFCs and can be treated as environmentally benign products.
The mechanism upon which the above described reactions take place whereby the perfluorocarbons are converted to iodoperfluoro and bromoperfluoro carbons is based upon the bond dissociation energies which are favorable to such conversion.
In accordance with a first embodiment of the present invention, a gas inlet receives a perfluorocarbon. The perfluorocarbon, along with possibly other reagents, is passed into a PECVD or plasma etch reactor wherein a processing step is effected with the effluent from the processing step still containing a perfluorocarbon. The effluent from the reactor is passed to a thermal chamber wherein the effluent containing the perfluorocarbon is mixed at a temperature greater than 800xc2x0 C. for a period of from about 1 to about 3 minutes with bromine-containing and/or iodine-containing compounds and/or bromine and/or iodine. The perfluorocarbon compound is reacted in the thermal chamber with the non-fluorine-containing halogen and/or halogen-containing compound to form halocarbons which contain iodine and/or bromine in addition to or without fluorine within the thermal chamber. Little or no perfluorocarbons containing which are otherwise halogen-free remain in the effluent from the chamber.
In accordance with a second embodiment of the present invention a gas inlet receives a perfluorocarbon. The perfluorocarbon, along with possibly other reagents, is passed into a PECVD or plasma etch reactor wherein a processing step is effected with the effluent from the processing step still containing a perfluorocarbon. The effluent from the reactor is passed to a plasma reactor wherein the effluent containing the perfluorocarbon is reacted with a plasma which is a bromine-containing and/or iodine-containing compound and/or bromine and/or iodine. All species will be dissociated by either plasma or heat and recombined to form energetically favorable non or less global warming species, whether non-fluorine or fluorohalogen, which will then be emitted to the atmosphere. The perfluorocarbon compound is reacted in the plasma reactor with the non-fluorine-containing halogen and/or halogen-containing compound to form halocarbons which contain iodine and/or bromine in addition to or without fluorine within the plasma reactor. Little or no perfluorocarbons containing no other halogen remain in the effluent from the reactor.